In order for unification the functors must match exactly. That is m
and n are two different functors hence the entire expression cannot
unify. In the first example the functors for both expressions are the
same.

this [workaround] doesn't seem very elegant.
std::atomic<T> cannot make arbitrary operations atomic: only
loading and storing the data is supported. That is why your
"workaround" is actually the way to deal with atomic objects: you
prepare the new node value in any way that you like, and then
atomically set it into an atomic<node> variable.
what if I have a pointer to an atomi

One method would be to set a unique index in mongodb on both the
nickname and the chatroom id. That would prevent inserts or updates
that would violate that index. You'd have to catch the errors in your
callback if you attempt to insert a nickname that currently exists.
http://docs.mongodb.org/manual/tutorial/create-a-unique-index/

The trouble is that when the child opens the file, it truncates it,
losing the data that the parent has already written to the file,
leaving the parent with a short count. It is likely that it will
always be the parent with the short count because the child has to
open the file a second time, and file opening is an expensive
operation. If the first open was moved so it was only in the parent,
th

The parent selector isn't a reference to the next level up, but the
entire composed selector after all imports/extends/mixin calls are
resolved.
.one {
.two {
.three & {
color: red;
}
}
}
The output will be this:
.three .one .two {
color: red;
}
In this example, & is equal to .one .two, not .two. It doesn't
matter what method you use to nest you